US20080309293A1, entitled “Method for Charging Battery Module in Multiple Stages,” discloses a method for charging a battery module in multiple stages. The method is configured for use with a battery module including a plurality of parallel-connected battery cells. US20080309293A1 discloses that the method is implemented by voltage control or current control to maintain a constant current for charging the battery module in an initial stage of charging. A charging current is lowered substantially to reduce the charging speed when the voltage of one of the parallel-connected battery cells exceeds a safety value or a total voltage of the battery module itself reaches a rated voltage. Accordingly, a safety problem of the battery can be avoided and meanwhile, the life span of the battery can be prolonged. However, the above technical solution disclosed in US20080309293A1 has a drawback; that is, lowering the charging current substantially to reduce the charging speed inevitably results in extending the duration of charging.
In light of the aforesaid drawbacks of the prior art, the inventor of the present invention is devoted to the improvement of the prior art and thus proposes a charging method and a charging device for use with a rechargeable battery with a view to shortening the duration of charging the rechargeable battery.